reserve n,i,k,m for Nat;
reserve r,r1,r2,s,s1,s2 for Real;
reserve p,p1,p2,q1,q2 for Point of TOP-REAL n;
reserve P,Q for Subset of TOP-REAL 2,
  f,f1,f2 for FinSequence of the carrier of TOP-REAL 2,
  p,p1,p2,p3,q,q3 for Point of TOP-REAL 2;

theorem
  f is special alternating & 1<=i & i+2<=len f implies LSeg(f,i) is
  vertical & LSeg(f,i+1) is horizontal or LSeg(f,i) is horizontal & LSeg(f,i+1)
  is vertical
by Th32,Th19,Th33;
